Born of moderately well-to-do parents, young Clay studied law under Chancellor George Wythe and was admitted to the Virginia bar in November 1797. He then moved to Lexington, Ky., a rising western community and a paradise for lawyers because of interminable lawsuits over land titles that were contested there. Endowed with great vitality, a ready but not profound intellect, and a gift for eloquent oratory, he was quick-witted and self-confident. Sociable, charming, and high-spirited, he loved to drink and gamble, qualities not distasteful to most of his contemporaries in Kentucky society. He was also hot-tempered, sensitive, and extremely ambitious.

Clay was spectacularly successful at the Kentucky bar in both civil and criminal cases, and he never lacked for clients. He acted as counsel for Aaron Burr (Burr, Aaron) (1806) in a Kentucky grand jury investigation of Burr's plan to establish an empire in the Southwest. Kentucky Republicans believed that Burr had been a victim of a Federalist conspiracy, and Clay's reputation did not suffer when his client's designs were later exposed.

Clay established his social position in 1799 by marrying Lucretia Hart, daughter of a wealthy Lexington businessman. By 1812 he possessed a 600-acre estate known as “Ashland,” where he bred livestock and raised hemp, corn (maize), and rye. He and Lucretia had 11 children, 6 daughters and 5 sons.

Clay entered politics shortly after arriving in Kentucky by championing liberalization of the state's constitution. A Jeffersonian Republican (Democratic-Republican Party), he shared that leader's distaste for slavery and was an advocate of gradual emancipation in Kentucky, but he abandoned this idea when it proved a losing cause. Like Jefferson, he learned to accept slavery, though, unlike him, he provided for the freeing of his slaves in his will. His eloquent opposition to the Alien and Sedition Acts of 1798, a series of repressive measures designed to curb the pro-French activities of the Jeffersonian Republicans, made Clay popular with Kentucky voters, and (1803–09) they elected him to seven terms in the state legislature.

Clay advocated the establishment of banks, internal improvements, and manufacturing, thus foreshadowing his future national career. Twice he went to Washington to fill out unexpired terms in the United States Senate, and in 1811 he was elected to the U.S. House of Representatives. There, as speaker (1811–14), he was one of the leaders who pushed the country into the War of 1812 (1812, War of). He also served as a member of the commission at Ghent that drew up the terms of peace with Britain in 1814.

During the next 10 years, Clay was Kentucky's outstanding representative in the U.S. Congress, usually serving as speaker of the House. Experience and a broadening outlook made him a neo-Jeffersonian Republican; he espoused internal improvements at national expense, a protective tariff, a national bank, and distribution of land-sale revenues to the states. Already he was developing a project of joining the industrial East and the agricultural West in a political alliance under the banner of his American System. He coveted appointment as secretary of state as a step toward the White House and was furious when Pres. James Monroe (Monroe, James) gave that post to John Quincy Adams. In 1819 he attacked Andrew Jackson (Jackson, Andrew) for his invasion of Florida, thus earning Old Hickory's lasting enmity. In 1820 he promoted the passage of the Missouri Compromise—which maintained the balance between the slave states and free states within the Union—and his followers began to call him “the great pacificator.” Then came one of the fateful crises in his career.

His four years in the state department were frustrating, largely because of the political machinations of the Jacksonians. Clay was thwarted in his effort to send delegates to a Pan American Congress at Panama, nor did he reach an accord with Great Britain on West Indian trade. Sneers at the “bargain” were hard to bear; a bitter attack on Clay by Congressman John Randolph led to a duel, in which neither man was wounded.

Clay remained in the Senate, leading an uphill fight against the policies of the Jacksonians and becoming a leader of the Whig Party, which gradually emerged in the middle 1830s. He refused to run for the presidency in 1836, when the Whigs put up sectional candidates, and it was with a heavy heart that he accepted reelection to the Senate in 1837. His mood changed with the panic of 1837 and the consequent rise of Whig fortunes. He confidently expected the party's nomination in 1840, but, to his bitter disappointment, the Whig politicians turned to a military hero, Gen. William Henry Harrison, who, with John Tyler (Tyler, John) of Virginia as his running mate, was easily elected.

Clay's hopes and plans had been thwarted, and his temper had not been improved by years of political frustration. He was now bent upon dictating his party's policies from his post in the Senate. He tried to dominate Harrison, who lived only a month after his inauguration, and was determined to do the same with Tyler. The latter, a stubborn man, vetoed two bank bills that had Clay's approval, and, when other items in the Kentuckian's program of legislation were challenged from both Congress and the White House, Clay resigned from the Senate in 1842.

Frustration continued to be Clay's lot. He opposed war with Mexico but supported its prosecution after the guns went off. He hoped for the Whig nomination in 1848, but the Whigs turned from their 71-year-old leader (even Kentucky refused to support him) and nominated a Mexican War hero, Gen. Zachary Taylor. Nevertheless, one last act of service to the nation remained for “the great pacificator.”

The annexation of territory in the Southwest heightened the strife between North and South over the extension of slavery, and Clay came back to the Senate in 1849 resolved to confront the growing threat of disunion. There in a great speech (Feb. 5–6, 1850) he outlined the principal features of what became the Compromise of 1850 (1850, Compromise of) and put the weight of his reputation and influence behind its passage. The compromise again kept the numerical balance between slave and free states and perhaps delayed the Civil War by a decade. This was his last act of statesmanship. His health failed, and he died of tuberculosis in the National Hotel at Washington, D.C., in 1852.

Clay was a man whose charm and nationalist fervour, coupled with the appeal of his ideas to the more conservative-minded, made him a national leader loved and honoured by many thousands of Americans. Mistakes of judgment, together with the skill and good fortune of his political opponents, kept him from reaching the White House, and the passage of the years has somewhat dimmed the aura that surrounded him while he lived. During the Civil War, President Lincoln and Secretary of State William H. Seward, discussing the political past, agreed that Clay's selfishness had injured the Whig Party, and historical scholarship has shown that the importance of his influence on the passage of the Compromise of 1850 was less than had been thought. But he was a staunch defender of the Union, a man who spent his life in public service and in that service helped to guide his country through some of the most difficult crises in its history.